1. Field of the Invention
This invention relates to methods and equipment for tertiary sewage treatment by naturally-occurring microorganisms after the sewage has passed from a septic tank or other primary treatment device.
2. Description of the Prior Art
Various sewage treatment systems are known for treating the waste stream from small communities, housing developments and single family units. With the establishment of state and federal guidelines, the need has become more acute for a system to handle sewage disposal needs where traditional methods do not work.
Septic tanks are the most commonly used means of treating sewage from a single source. They employ anaerobic bacteria for the primary decomposition of sewage, separating some solid wastes from liquid. The liquid waste streams from septic tanks are often discharged directly to the entry of a subsurface drain field. The remainder of wastewater treatment occurs in the soil. However, many sites and many soil types are unable to accomplish this process in a manner that meets applicable guidelines.
Tertiary treatment systems employ processes in which anaerobic decomposition is followed by aerobic decomposition. Tertiary systems lessen the burden on the land, as soils are no longer being called upon to treat wastewater.
A secondary treatment method wherein aerobic processes are augmented, for example, by a flow of gas through the material to be treated, is known from U.S. Pat. No. 3,202,285. It has also been proposed to use a gravel bed in secondary treatment, as set forth in U.S. Pat. Nos. 3,057,796 and 4,293,421.
U.S. Pat. No. 5,597,477 contains a description of a sewage effluent disposal system comprising a primary sewage treatment tank and an effluent holding tank. A float switch controls the pumping of effluent from the effluent holding tank. Secondary treatment is accomplished by passing the effluent through a sparger as it enters the secondary treatment tank, or by adding disinfectant as the effluent passes through the sparger. The secondary treatment tank does not contain a filtration bed.
It is an object of the present invention to provide a wastewater treatment system in which tertiary treatment occurs in enclosed, controlled conditions rather than in surrounding soils, so that the invention can be used where soils are marginal or cannot be used with other systems.
The tertiary treatment recirculation process may be controlled by a timer and a pump float responding to the wastewater level in the recirculation tank, thus providing an automated control system.
Another object of the invention is to provide a wastewater treatment system as described in the preceding paragraphs in which the effluent is safe and environmentally acceptable. Yet another object of the invention is to provide a durable wastewater treatment system, requiring minimal maintenance, and in which repair and regeneration are readily accomplished.